Light-emitting element and display device

ABSTRACT

There has been a problem that difference in refractive index between an opposite substrate or a moisture barrier layer (passivation film) such as SiN provided thereover, and air is maintained large, and light extraction efficiency is low. Further, there has been a problem that peeling or cracking due to the moisture barrier layer is easily generated, which leads to deteriorate the reliability and lifetime of a light-emitting element. According to the present invention, a light-emitting element comprises a pixel electrode, an electroluminescent layer, a transparent electrode, a passivation film, a stress relieving layer, and a low refractive index layer, all of which are stacked sequentially. The stress relieving layer serves to prevent peeling of the passivation film. The low refractive index layer serves to reduce reflectivity of light generated in the electroluminescent layer in emitting to air. Therefore, a light-emitting element with high reliability and long lifetime and a display device using the light-emitting element can be provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/733,331, filed Apr. 10, 2007, now allowed, which is a continuation ofU.S. application Ser. No. 11/131,437, filed May 18, 2005, now U.S. Pat.No. 7,202,504, which claims the benefit of a foreign priorityapplication filed in Japan as Serial No. 2004-151036 on May 20, 2004,all of which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting element as typified byan organic EL element and a display device having the light-emittingelement.

2. Related Art

In recent years, a display device having a light-emitting element astypified by an organic EL (Electro Luminescence) element has beendeveloped and expected to be widely used with taking advantages of ahigh quality image, a wide viewing angle, and a slim and lightweightshape due to that the display device is a self-luminous type. The “ELelement” refers to a light-emitting element that uses a principle thatan electroluminescent layer emits light that is interposed between apair of electrodes by applying current to an anode and a cathode. As thelight-emitting element, for example, a so-called top emissionlight-emitting element having a transparent electrode at a side of anopposite substrate to emit light to the side of the opposite substrateis known. FIG. 17 illustrates a cross-sectional view of the top emissionlight-emitting element. In FIG. 17, reference numeral 1 denotes asubstrate; 2, an electrode; 3, a hole transporting layer; 4, alight-emitting layer; 5, an electron injecting layer; 6, a transparentelectrode; 7, a moisture barrier layer; and 8, an antireflection layer.The light-emitting element utilizes light that is radiated when anexciton that is generated by the recombination of electrons injected tothe light-emitting element 4 from the transparent electrode 6 via theelectron injecting layer 5 and holes injected to the light-emittinglayer 4 from the electrode 2 via the hole transporting layer 3 returnsto the ground state.

The light-emitting element that extracts light from a top side (oppositesubstrate side) such as a top emission light-emitting element isrequired to use the transparent electrode 6 as an opposite electrode.For example, an indium tin oxide (ITO) or the like is used, in whichcase there is a problem that light extraction efficiency is deterioratedsince there is large difference in refractive indexes of the transparentelectrode 6 and air around the transparent electrode 6 (patent documents1 and 2).

Further, a light-emitting element including an organic compound as itsmain constituent is subject to be deteriorated mainly due to moisture oroxygen. As deterioration due to the moisture or oxygen, luminance ispartly lowered or a non emission region is produced. In order to preventthe deterioration, technique of forming a passivation film (moisturebarrier layer 7) such as a SiN film for moisture barrier over thetransparent electrode 6 is known (a patent document 2). However, thereis a problem that light-extraction efficiency is deteriorated sincethere is large difference in refractive indexes between the SiN film andair even in the case that the passivation film (moisture barrier layer7) such as a SiN film for moisture barrier is formed over thetransparent electrode 6 (a patent document 2).

Technique of forming a film made from a material having a lowerrefractive index than that of the transparent electrode 6 as anantireflection film 8 in a signal layer or a multi-layer over thetransparent electrode 6 or the moisture barrier layer 7 is known towardthe foregoing problems (patent documents 1 and 2).

Patent document 1: Unexamined Patent Publication No. 2003-303679

Patent document 2: Unexamined Patent Publication No. 2003-303685

The refractive index of the transparent electrode 6, for example, ITO,is approximately 1.9 to 2.0, whereas the refractive index of themoisture barrier layer 7, for example, a SiN film, formed over thetransparent electrode 6 is approximately 2.1 to 2.3, which is higherthan that of the transparent electrode 6. In the case that the moisturebarrier layer 7 such as a SiN film is formed over the transparentelectrode 6, there is still large difference in refractive indexesbetween the moisture barrier layer 7 and the antireflection layer 8 evenwhen the antireflection layer 8 having a lower refractive index thanthat of the transparent electrode 6 is formed over the moisture barrierlayer 7. Therefore, the reflectivity of an interface between themoisture barrier layer 7 and the antireflection layer 8 is furtherincreased compared to the case that the moisture barrier layer 7 is notprovided. Therefore, there is a problem that light extraction efficiencyfrom the light-emitting layer is deteriorated with the increase ofreflection loss of light at the interface.

In the case of forming the moisture barrier layer 7, there is a problemthat peeling, cracking, and the like due to stress are often occurred,which leads to deterioration of manufacturing yields, lower reliability,and reduction of lifetime of a light-emitting element.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve at least one problemamong the foregoing problems. It is more specific object of the presentinvention to provide a light-emitting element having high reliabilityand a display device using the light-emitting element resistant topeeling, cracking, or the like even if a passivation film is providedover a transparent electrode. It is another object of the presentinvention to provide a light-emitting element that has high lightextraction efficiency from a light-emitting layer and a display deviceusing the light-emitting element. It is further another object of thepresent invention to provide a light-emitting element that can solve allof the foregoing problems simultaneously and a display device using thelight-emitting element.

According to the present invention, a light-emitting element comprises apixel electrode, an electroluminescent layer, a transparent electrode, apassivation film, a stress relieving layer, and a low refractive indexlayer, all of which are stacked sequentially. The stress relieving layerserves to prevent peeling of the passivation film. The low refractiveindex layer serves to reduce reflectivity of light generated in theelectroluminescent layer in emitting to air to improve light extractionefficiency. Each of the pixel electrode and the transparent electrodeserves as an anode or a cathode for supplying electrons or holes to theelectroluminescent layer. The passivation film serves to preventimpurities such as moisture from penetrating into the transparentelectrode or the electroluminescent layer. The passivation film, thestress relieving layer, or the low refractive index layer may have alamination layer structure. Further, the stress relieving layer may beprovided between the transparent electrode and the passivation film. Theelectroluminescent layer may have a single layer structure or alamination layer structure.

According to the present invention, a light-emitting element comprises apixel electrode, an electroluminescent layer, a transparent electrode, apassivation film, a stress relieving layer, and a low refractive indexlayer, all of which are stacked sequentially, in which a refractiveindex of the low refractive index layer is smaller than that of thestress relieving layer. The low refractive index layer serves to reducethe difference in refractive indexes between the stress relieving layerand space. (The space is filled with a filling gas such as air ornitrogen. The same applies hereinafter.)

According to the present invention, a light-emitting element comprises apixel electrode, an electroluminescent layer, a transparent electrode, astress relieving layer, a passivation film, and a low refractive indexlayer, all of which are stacked sequentially.

According to the present invention, a light-emitting element comprises apixel electrode, an electroluminescent layer, a transparent electrode, afirst stress relieving layer, a passivation film, a second stressrelieving layer, and a low refractive index layer, all of which arestacked sequentially. A refractive index of the low refractive indexlayer may be smaller than that of the second stress relieving layer.

According to the present invention, a display device comprises atransistor provided over a substrate; and a light-emitting elementconnected to the transistor via an interlayer insulating film; whereinthe light-emitting element is formed by sequentially stacking a pixelelectrode, an electroluminescent layer, a transparent electrode, apassivation film, a stress relieving layer, and a low refractive indexlayer. Here, the transistor serves to control ON/OFF of thelight-emitting element; however, a transistor having another functionmay be included in the display device. As the transistor, a thin filmtransistor (TFT) is, but not exclusively, used generally. The interlayerinsulating film is an insulating film that separates the transistor fromthe light-emitting element. The interlayer insulating film may haveeither a single layer structure or a lamination layer structure. Thestress relieving layer serves to prevent peeling of the passivationfilm. The low refractive index layer serves to reduce reflectivity oflight generated in the electroluminescent layer in emitting to air toimprove light extraction efficiency. A refractive index of the lowrefractive index layer is preferably smaller than that of the stressrelieving layer. Each of the pixel electrode and the transparentelectrode serves as an anode or a cathode for supplying electrons orholes to the electroluminescent layer. The passivation film serves toprevent impurities such as moisture from penetrating into thetransparent electrode or the electroluminescent layer. The passivationfilm, the stress relieving layer, or the low refractive index layer mayhave a lamination layer structure.

According to the present invention, a display device comprises atransistor provided over a substrate; and a light-emitting elementconnected to the transistor via an interlayer insulating film; whereinthe light-emitting element is formed by sequentially stacking a pixelelectrode, an electroluminescent layer, a transparent electrode, astress relieving layer, a passivation film, and a low refractive indexlayer.

According to the present invention, a display device comprises atransistor provided over a substrate; and a light-emitting elementconnected to the transistor via an interlayer insulating film; whereinthe light-emitting element is formed by sequentially stacking a pixelelectrode, an electroluminescent layer, a transparent electrode, a firststress relieving layer, a passivation film, a second stress relievinglayer, and a low refractive index layer; and a refractive index of thelow refractive index layer is smaller than that of the second stressrelieving layer.

In the display device according to the present invention, thelight-emitting element may be sealed with an opposite substrate via afilling layer. Here, a refractive index of the filling layer ispreferably almost the same as that of refractive indexes of a lowrefractive index layer and an opposite substrate or intermediate betweenthose of the low refractive index layer and the opposite substrate. Thefilling layer may be a liquid layer or a solid layer that has at least alager refractive index than that of air (or a filling gas such asnitrogen).

The light-emitting element according to the present invention canincrease the thickness of a passivation film without being adverselyaffected by peeling, cracking, or the like of the passivation film sincea stress relieving layer is formed on a top surface or a bottom surfaceof the passivation film. As a result, an extreme high blocking effectcan be obtained. Therefore, a light-emitting element having highreliability and long lifetime can be provided at high manufacturingyields.

In the case that the stress relieving layer is formed over a top surface(both surfaces) of the passivation film, the difference in refractiveindexes between the stress relieving layer and air can be reduced byforming the low refractive index layer to have a lower refractive indexthan that of the stress relieving layer. As a result, efficiency oflight extraction to the outside can be improved.

The display device according to the present invention can increase thethickness of a passivation film without being adversely affected bypeeling, cracking, or the like of the passivation film since alight-emitting element has a stress relieving layer over a top surfaceor a bottom surface of the passivation film. As a result, an extremehigh blocking effect can be obtained. Therefore, a display device havinghigh reliability and long lifetime can be provided at high manufacturingyields.

In the case that the low refractive index layer is formed to have alower refractive index than that of the stress relieving layer, thedifference in refractive indexes between the stress relieving layer andair can be reduced. Moreover, efficiency of light extraction to theoutside can be further improved in the case that a filling layer isformed between the low refractive index layer and the oppositesubstrate.

These and other objects, features and advantages of the presentinvention will become more apparent upon reading of the followingdetailed description along with the accompanied drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are explanatory views for showing a structure of alight-emitting element according to the present invention;

FIG. 2 is an explanatory view for showing a structure of alight-emitting element according to the present invention (in which afilling layer is provided);

FIGS. 3A and 3B are explanatory views for showing a structure of alight-emitting element according to the present invention (in which astress relieving layer is provided at the bottom of a passivation film);

FIGS. 4A and 4B are equivalent circuit diagrams of a pixel region of adisplay device according to the present invention and a top view of adisplay panel of the display device, respectively;

FIGS. 5A and 5B are cross-sectional views for showing a display deviceaccording to the present invention;

FIGS. 6A and 6B are cross-sectional views for showing a display deviceaccording to the present invention (in which a color filter isprovided);

FIGS. 7A and 7B are cross-sectional views for showing a display deviceaccording to the present invention (in which a low refractive indexlayer is provided to an opposite substrate);

FIGS. 8A and 8B are equivalent circuit diagrams of a pixel region of adisplay device according to the present invention;

FIGS. 9A to 9D are cross-sectional views for showing a wiring formed tohave a lamination layer structure;

FIGS. 10A to 10F are views for showing electric appliances using displaydevices according to the present invention;

FIG. 11 is a block diagram for showing a main structure of a televisionset using a display device according to the present invention;

FIGS. 12A and 12B are explanatory views of an ID card using a displaydevice according to the present invention;

FIG. 13 is a top view of a light-emitting device according to thepresent invention;

FIG. 14 is a view of showing a circuit for operating one pixel in alight-emitting device according to the present invention;

FIG. 15 is a top view of a pixel region in a light-emitting deviceaccording to the present invention;

FIG. 16 is an explanatory view of an operation of a frame with time;

FIG. 17 is an explanatory view of a structure of a conventionallight-emitting device; and

FIG. 18 is an explanatory view of a method for selecting a plurality ofgate signals simultaneously in one horizontal period.

DESCRIPTION OF THE INVENTION

Embodiments according to the present invention will be explained indetail with reference to the drawings. Through the drawings of theembodiments, like components are denoted by like numerals in common withthe different drawings.

As used herein, the term “light-emitting element” refers to an elementthat comprises a passivation film, a stress relieving film, a lowrefractive index layer, and the like, which are characterizing portionsof the present invention, formed over an anode or a cathode, in additionto a general element that comprises a electroluminescent layerinterposed between the anode and the cathode. In other words, the term“light-emitting element” includes the portion that serves to decrease arefractive index of a portion through which light passes and relievestress of the passivation film. In the case of explaining variouscompound materials by using a chemical formula in this specification, amaterial having an arbitrary composition ratio can be appropriatelyselected unless otherwise stated (for example, “SiN” means SixNy (x,y>0). Further, the refractive index may be abbreviated to “n” in thisspecification.

Embodiment 1

A structure of a light-emitting element according to this embodiment isexplained with reference to FIG. 1A. FIG. 1A illustrates a schematiccross-sectional view of the light-emitting element according to thisembodiment. The light-emitting element according to this embodimentcomprises a pixel electrode 11, an electroluminescent layer 12, atransparent electrode 13, a passivation film 14, a stress relievinglayer 15, and a low refractive index layer 16 as illustrated in FIG. 1A.The light-emitting element is generally provided over a substrate 10.The light-emitting element according to this embodiment is capable ofemitting light to the top (so-called top emission), which comprises thepassivation film 14 formed over the transparent electrode 13, the stressrelieving layer 15 formed over the passivation film 14, and the lowrefractive index layer 16 formed over the stress relieving layer 15. Thepresent invention can be applied to a top emission light-emittingelement and a dual emission light-emitting element by which light isemitted to top and bottom surfaces of a light-emitting layer. FIG. 1Aillustrates only light emitted to the top for descriptive purposes.Hereinafter, the light-emitting element is explained specifically.

The substrate 10 is a substrate having an insulating surface made from,but not exclusively, glass, quartz, plastic, or the like. In the case ofusing a plastic substrate, any substrate having flexibility can be used.For instance, a substrate made from one kind plastic selected from thegroup consisting of polyethylene terephthalate (PET), polyether sulfone(PES), polyethylenenaphthalate (PEN), polycarbonate (PC), nylon,polyetheretherketone (PEEK), polysulfone (PSF), polyetherimide (PEI),polyarylate (PAR), polybutylene terephthalate (PBT), and polyimide.

The pixel electrode 11 is provided over the substrate 10. The topemission type uses a metal material having reflectivity as the pixelelectrode 11 despite of the polarity of the pixel electrode 11. Forinstance, in the case that the pixel electrode 11 serves as a cathode, atransparent conductive film formed by co-evaporation of an element suchas Al, AlLi, MgAg, MgIn, Ca, or an element belonging to 1 or 2 group inthe periodic table, and aluminum. These materials are suitable for acathode material since they have small work functions and electrons areeasily extracted therefrom. In this case, the light-emitting element isformed by sequentially stacking the cathode, an electroluminescentlayer, and an anode over the substrate. The lamination layer structureis referred to as a reverse stacked structure.

In the case that the pixel electrode 11 serves as an anode, an elementselected from the group consisting of Cr, Ti, TiN, TiSixNy, Ni, W, WSix,WNx, WSixNy, NbN, Pt, Zn, Sn, In, and Mo, or a film or a laminated filmmade from an alloy material or a compound material containing theforegoing elements as its main component may be used for the pixelelectrode 11. In this case, the light-emitting element is formed bystacking sequentially an anode, an electroluminescent layer, and acathode over a substrate. The lamination layer structure is referred toas a forward stacked structure.

On the other hand, a dual emission type uses a metal material having alight transmitting property as the pixel electrode 11 since light isrequired to be emitted to the bottom. Typically, ITO is used. ITO isgenerally used as an anode, in which case a structure of alight-emitting element is a forward stacked structure. In the case thatthe pixel electrode serves as a cathode, ITO is used to ensuretransparency, and a thin film such as Li that is a cathode material maybe formed between the ITO and the electroluminescent layer 12. Insteadof ITO, a transparent conductive film such as ITSO (indium tin siliconoxide, mixture of ITO and silicon oxide), ZnO (zinc oxide), GZO (zincoxide doped with gallium), or IZO (indium zinc oxide, mixture of anindium oxide and a zinc oxide of approximately 1 to 20%) can be used.

Further, a barrier layer including silicon, silicon oxide, siliconnitride, or the like can be interposed between the transparentconductive film such as ITO and the electroluminescent layer 12.Accordingly, it is experimentally found that luminous efficiency isincreased. The pixel electrode 11 may be an electrode having anantireflection function formed by covering a Cr film or the like both oreither of surfaces of the ITO or the like. Hence, outside light oremission of light can be prevented from reflecting off the pixelelectrode 11 and interfering with light extracted to the outside.

The electroluminescent layer 12 is formed over the pixel electrode 11.In the case of forward stacked structure, the electroluminescent layer12 may have a lamination layer structure composed of a hole transportinglayer 3, a light-emitting layer 4, and an electron injecting layer 5 asdescribed in the conventional example (FIG. 17), alternatively, theelectroluminescent layer 12 may have a single layer structure composedof only a light-emitting layer. In the case of forming theelectroluminescent layer 12 by a plurality of layers, theelectroluminescent layer 12 may have the structure formed by stackingsequentially 1) anode/hole injecting layer/hole transportinglayer/light-emitting layer/electron transporting layer/cathode, 2)anode/hole injecting layer/light-emitting layer/electron transportinglayer/cathode, 3) anode/hole injecting layer/hole transportinglayer/light-emitting layer/electron transporting layer/electroninjecting layer/cathode, 4) anode/hole injecting layer/hole transportinglayer/light-emitting layer/hole blocking layer/electron transportinglayer/cathode, 5) anode/hole injecting layer/hole transportinglayer/light-emitting layer/hole blocking layer/electron transportinglayer/electron injecting layer/cathode, or the like. The foregoingstructures are forward stacked structures. In the case of forming areverse stacked structure, the order of stacking may be reversed.

The electroluminescent layer 12 that can be thought as a center of alight-emitting element is generally composed of an organic compoundlayer. All of the foregoing hole injecting layer, hole transportinglayer, light-emitting layer, electron transporting layer, electroninjecting layer, and the like are included in the electroluminescentlayer 12. As a material for composing the electroluminescent layer 12, alow molecular organic or inorganic compound material, an intermediatemolecular organic or inorganic compound material, or a high molecular(polymer) organic or inorganic compound material can be used,alternatively, a material that is combination of the foregoing materialscan be used. Generally, the handling of the high molecular organiccompound material is easier, and heat resistance of the high molecularorganic compound material is higher than those of the low molecularorganic compound material. Further, a mixed layer that is formed byappropriately mixing the electron transporting material to the holetransporting material or a mixed junction formed by providing a mixedregion to each connection interface can be formed. A fluorescent dye orthe like can be doped to the light-emitting layer. As a method fordepositing the organic compounds, a vapor deposition method, a spincoating method, and an ink jetting method are known. Especially, thespin coating method or the ink jetting method is preferably used torealize full color display with the use of a high molecular material.

In order to improve reliability, deaeration is preferably carried out byvacuum heating (100 to 250° C.) immediately prior to forming theelectroluminescent layer 12. For instance, vapor deposition is carriedout in a deposition chamber that is evacuated to vacuum of 0.665 Pa(5×10⁻³ Torr) or less, preferably, 1.33×10⁻² to 1.33×10⁻⁴(10⁻⁴ to 10⁻⁶Torr). In a vacuum deposition process, an organic compound is vaporizedin advance by resistance heating to disperse in the direction of asubstrate upon opening a shutter. The vaporized organic compounddisperses upward to be deposited over a substrate through an openingportion provided to a metal mask. For instance, white emission can beobtained by stacking sequentially Alq₃ (hereinafter, Alq₃ may bereferred to as Alq), Alq₃ partly doped with Nile red that is a redemission dye, p-EtTAZ, and TPD (aromatic diamine) by a vapor depositionmethod.

In the case that the electroluminescent layer 12 is formed by a coatingmethod using a spin coating method, a material is preferably baked byvacuum heating after the material is coated. For instance, an aqueoussolution of poly(ethylene dioxythiophene)/poly(styrene sulfonic acid)(PEDOT/PSS) that serves as a hole injecting layer may be applied to anentire surface to be baked. Then, a polyvinyl carbazole (PVK) solutiondoped with a luminescent center pigment (such as1,1,4,4-tetraphenyl-1,3-butadiene (TPB),4-dicyanomethylene-2-methyl-6-(p-dimethylamino-styryl)-4H-pyran (DCM1),Nile red, or coumarin 6) that serves as a light emitting layer may becoated over the entire surface to be baked. Water is used as the solventof PEDOT/PSS. The PEDOT/PSS is not soluble in an organic solvent.Accordingly, the PEDOT/PSS is not resoluble even when PVK is coatedthereover. Since the solvents used for PEDOT/PSS and PVK are differentfrom each other, the PEDOT/PSS and the PVK do not preferably share onechamber. The electroluminescent layer 12 can be formed to have a singlelayer, in which case, a 1,3,4-oxadiazole derivative (PBD) having anelectron transporting property may be dispersed in polyvinyl carbazole(PVK) having a hole transporting property. In addition, white lightemission can be obtained by dispersing 30 wt % of PBD as an electrontransporting agent and dispersing four kinds of pigments (TPB, coumarin6, DCM1, and Nile red) in appropriate amounts.

An example of a light-emitting element exhibiting white emission isexplained here. Needless to say, a light-emitting element that canexhibit red emission, green emission, or blue emission can bemanufactured by selecting appropriately materials of theelectroluminescent layer 12, in which case, a color filter asillustrated in FIG. 6 can be omitted. The emission mechanism of alight-emitting element is generally considered that voltage is appliedto an organic compound layer interposed between a pair of electrode, andelectrons injected from a cathode and holes injected from an anode arerecombined with each other in an emission center in an organic compoundlayer to form molecular excitons, then, the molecular excitons radiateenergy to emit light while returning to a ground state. An excited stateis known as a single excitation and a triplet excitation, both of whichcan be applied to a light-emitting element according to the presentinvention.

For instance, light emission (phosphorescence) from a triplet excitationstate is used, CBP+Ir (ppy)₃ made from carbazole can be used as anorganic compound (also referred to as a triplet compound) that canexhibits phosphorescence. The phosphorescence has advantages of havinghigher luminous efficiency than that of emission (fluorescence) from asinglet excitation state and capable of operating emitting light at thesame level of luminance as fluorescence at lower operation voltage (thatis required to emit an organic light-emitting element).

A transparent electrode 13 is formed over the electroluminescent layer12. In the case that the transparent electrode 13 serves as an anode, atransparent conductive film such as ITO may be used. On the other hand,in the case that the transparent electrode 13 serves as a cathode, athin film such as Li that is a cathode material may be formed betweenthe transparent electrode 13 and the electroluminescent layer 12.

A passivation film 14 is formed over the transparent electrode 13. Thepassivation film 14 is preferably formed by a single layer or alamination layer made from silicon nitride (typically, Si₃N₄), siliconoxide (typically, SiO₂), silicon nitride oxide (SiNO (composition ratio:N>O)), silicon oxynitride ((composition ratio: N<O)), thin filmincluding carbon as its main component (DLC (Diamond Like Carbon) film,CN film, and the like), or the like. The passivation film 14 made fromnitrides has fine membrane quality, and so it protects the transparentelectrode 13 and has an extreme high blocking effect against moisture,oxygen, and impurities, which deteriorate the electroluminescent layer12.

As noted above, the passivation film 14 has a high blocking effect;however, the passivation film 14 is subject to peeling or cracking whenthe thickness and the membrane stress are increased. The peeling and thelike of the passivation film can be prevented by providing the stressrelieving layer 15 over the passivation film 14. As the stress relievingfilm 15, an organic material or an inorganic material having smallstress is appropriately selected to be used. It is preferable that thematerial for the stress relieving film has a lower refractive index thanthat of the transparent electrode 13 or the passivation film 14. Forinstance, polyimide resin, acrylic resin, or styrene resin can be used.Moreover, polyamide, polyimideamide, resist or benzocyclobutene, or anSOG film obtained by a coating method (for example, an SiOx filmincluding a an alkyl group formed by a coating method using a siloxanecoated film (The siloxane is composed of a skeleton formed by the bondof silicon (Si) and oxygen (O), in which an organic group containing atleast hydrogen (such as an alkyl group or aromatic hydrocarbon) isincluded as a substituent. Alternatively, a fluoro group may be used asthe substituent. Further alternatively, a fluoro group and an organicgroup containing at least hydrogen may be used as the substituent.) orSiOx film using a polysilazane coated film) or a material that isidentical or similar to an organic material used for theelectroluminescent layer can be used.

As described above, the thickness of the passivation film 14 can beincreased without being adversely affected by pealing or cracking of thepassivation film 14 by providing the stress relieving layer 15. As aresult, an extreme high blocking effect can be obtained. A material forforming the stress relieving film includes a material serving as thepassivation film 14. When the stress relieving film is made from suchthe material serving as the passivation film 14, the stress relievingfilm can be included in a stress relieving film as long as the formedstress relieving film has a function as a stress relieving film (thatis, a function capable of preventing pealing, cracking, or the like as aresult or a function of preventing pealing, cracking, or the like or afunction capable of preventing pealing, cracking, or the like actuallyby being formed over a material having a comparative large membranestress). For instance, the case that SiO₂ (refractive index n isapproximately equal to 1.5) or SiNO (n is approximately equal to 1.8) isformed as a stress relieving layer (and a passivation layer) in the casethat SiN (refractive index n is equal to 2.1 to 2.3) is formed as thepassivation film can be nominated.

The low refractive index layer 16 is provided over the stress relievinglayer 15. As used herein, the term “low refractive index layer” refersto a layer having a lower refractive index than that of the stressrelieving layer 15 and a higher refractive index than that of theoutside atmosphere of the light-emitting element (generally, n is equalto 1). The outside atmosphere may be air or atmosphere filled withnitrogen gas or the like.

In the case that the stress relieving layer 15 is formed over thepassivation film 14, suppose that refractive indexes of the transparentelectrode 13, the passivation film 14, the stress relieving layer 15,and the low refractive index layer 16 are n_(T), n_(P), n_(B), andn_(L), respectively, the relationships of the refractive indexes arepreferably as follows.

1) If n_(T)<n_(P), n_(P)>n_(B)>n_(L) is fulfilled.

2) If n_(T)>n_(P), n_(T)>n_(B)>n_(L) is fulfilled.

More preferably, n_(P)>n_(B)>n_(L) or n_(P)≈n_(B)>n_(L) (that is, therelation that the refractive index is gradually lowered from thetransparent electrode 13 to the refractive index layer 16 is fulfilled).

In the case of using ITO as the transparent electrode 13, the refractiveindex is 1.9 to 2.0. In the case of using SiN as the passivation film14, the refractive index is 2.1 to 2.3. In the case of using SiNO as thepassivation film 14, the refractive index is approximately 1.8. In thecase of using SiO₂ as the passivation film 14, the refractive index isapproximately 1.5. Therefore, the following are the refractive indexesof materials used for forming the stress relieving film 15, that is,polyimide resin (n=1.50 to 1.55), acrylic resin (n=1.45 to 1.50),styrene resin (n=1.55 to 1.60), magnesium fluoride (MgF₂, n=1.38 to1.40), barium fluoride (BaF₂, n=1.47), and an organic material used foran electroluminescent layer (n is approximately equal to 1.6). Further,MgO (n=1.64 to 1.74), SrO₂, and SrO are suitable for the stressrelieving layer 15 since they have a light-transmitting property and ahygroscopic property and can be formed into a thin film by vapordeposition.

In the case that an organic material is used for forming the stressrelieving layer 15, α-NPD4,4′-bis(N-(1-naphthyl)-N-phenylamino)biphenyl, BCP (bathocuproine),MTDATA 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine,Alq₃ (tris(8-quinolinolato)aluminum complex, or the like can be used asthe organic material. The foregoing organic materials have a hygroscopicproperty and almost transparent if the material is formed to have a thinfilm thickness.

As the low refractive index layer 16, a material that has a lowerrefractive index than that of the stress relieving layer 15 such aslithium fluoride (LiF, n=1.30 to 1.39), magnesium fluoride (MgF₂, n=138to 1.40), calcium fluoride (CaF₂, n=1.23 to 1.45), or barium fluoride(BaF₂, n=1.47) may be used.

Materials for the transparent electrode 13, the passivation film 14, thestress relieving layer 15, and the low refractive index layer 16 are notlimited to the foregoing materials. Any material that fulfills therelations of 1) and 2) can be used. The material used that fulfills anyrelation among the foregoing inequations 1) and 2) with respect to therefractive indexes of the transparent electrode 13, the passivation film14, the stress relieving layer 15, and the low refractive index layer 16can reduce the difference in refractive indexes of interfaces betweenthese layers and improve light extraction efficiency to the outside.

The transparent electrode 13, the passivation film 14, the stressrelieving layer 15, and the low refractive index layer 16 can be formedby a sputtering method, a CVD method, a vapor deposition method, or thelike. For instance, it is preferable that the transparent electrode 13is formed by a sputtering method, the passivation film 14 is formed by aCVD method, and the stress relieving layer 15 and the low refractiveindex layer 16 are formed by a vapor deposition method. In this case, byadopting a multi-chamber system composed of an integrated combination ofa sputter deposition chamber, a CVD deposition chamber, vapor depositionchamber, and a bake chamber for drying processing, film formation can beefficiently carried out by transporting a substrate to each of thechambers.

As described above, a light-emitting element according to the presentinvention has the stress relieving layer 15 over the passivation film14, and so the thickness of the passivation film 14 can be increasedwithout being adversely affected by the peeling and cracking of thepassivation film 14. As a result, an extreme high blocking effect can beobtained.

The stress relieving layer 15 has a refractive index intermediatebetween those of the passivation film 14 or the transparent film 13, andthe low refractive index layer 16, and so the stress relieving layer 15can reduce the difference in refractive indexes of interfaces betweenthe transparent electrode 13, the passivation film 14, the stressrelieving layer 15, and the low refractive index layer 16.

A light-emitting element according to the present invention can beadopted in a light-emitting device as typified by an EL display. Thelight-emitting device can be broadly divided into two kinds, that is, asimple matrix system in which an electroluminescent layer is formedbetween two kinds of stripe-shaped electrodes provided so as to be rightangles with each other, and an active matrix system in which anelectroluminescent layer is formed between a pixel electrode and anopposite electrode arranged in a matrix configuration and connected toTFT. The light-emitting element according to the present invention canbe applied to either of the simple matrix system and the active matrixsystem.

Embodiment 2

A structure of a light-emitting element according to this embodiment isexplained with reference to FIG. 1B. FIG. 1B is a schematiccross-sectional view of the light-emitting element according to thisembodiment. The characteristic feature of the present invention relatingto this embodiment is a passivation film 14 having a lamination layerstructure. The structure illustrated in FIG. 1B has a three-layerstructure formed by stacking sequentially a silicon nitride film 14 a, asilicon oxide film 14 b, and a silicon nitride film 14 c. The secondlayer, SiO₂ film, combines a function as a passivation film and afunction of preventing peeling or cracking of a SiN film (function as astress relieving film). By forming the passivation film to have athree-layer structure, a barrier property of the passivation film isimproved and penetration of impurities such as moisture or oxygen into atransparent electrode 13 or an electroluminescent layer 12 can beeffectively prevented.

A structure of the passivation film 14 is not limited to thatillustrated in FIG. 1B. The passivation film 14 is preferably formed tohave a structure so that difference in refractive indexes of interfacesof layers that construct the passivation film 14. Moreover, a stressrelieving layer 15 and a low refractive index layer 16 are formed overthe passivation layer 14. The stress relieving layer 15 only has tofulfill the relations of 1) and 2) in Embodiment 1 with respect to thetop layer of the passivation film 14. In the case that the stressrelieving layer 15 is formed to have a lamination layer structure usingthe material described in Embodiment 1, the low refractive index layer16 only has to fulfill the relations of 1) and 2) in Embodiment 1 withrespect to the top layer of the stress relieving layer 15. The otherstructure of the light-emitting element according to this embodiment canbe referred to Embodiment 1.

Because of forming the passivation film 14 to have a laminationstructure, the light-emitting element according to the present inventionhas an improved barrier property and can prevent effectively impuritiessuch as moisture or oxygen from penetrating into the transparentelectrode 13 or the electroluminescent layer 12. The light-emittingelement has the stress relieving layer 15 over the passivation film 14,and so the thickness of the passivation film 14 can be increased withoutbeing adversely affected by the peeling and cracking of the passivationfilm 14. As a result, an extreme high blocking effect can be obtained.

The stress relieving layer 15 has a refractive index intermediatebetween those of the passivation film 14 or the transparent film 13, andthe low refractive index layer 16 according to the relations of 1) and2) in Embodiment 1, and so the stress relieving layer 15 can reduce thedifference in refractive indexes of interfaces between the transparentelectrode 13, the passivation film 14, the stress relieving layer 15,and the low refractive index layer 16.

A light-emitting element according to the present invention can beadopted in a light-emitting device as typified by an EL display. Thelight-emitting device can be broadly divided into two kinds, that is, asimple matrix system in which an electroluminescent layer is formedbetween two kinds of stripe-shaped electrodes provided so as to be rightangles with each other, and an active matrix system in which anelectroluminescent layer is formed between a pixel electrode and anopposite electrode arranged in a matrix configuration and connected toTFT. The light-emitting element according to the present invention canbe applied to either of the simple matrix system and the active matrixsystem.

Embodiment 3

A structure of a light-emitting element according to this embodiment isexplained with reference to FIG. 2. FIG. 2 is a schematiccross-sectional view of the light-emitting element according to thisembodiment. The characteristic feature of the present invention relatingto this embodiment is that space between a low refractive index layer 16and an opposite substrate 18 is filled with a filling layer 17. Thefilling layer 17 has preferably a refractive index that is almost thesame as those of a low refractive index layer 16 and an oppositesubstrate 18 or that is intermediate between those of the low refractiveindex layer 16 and the opposite substrate 18. In the case that the lowrefractive index layer 16 is made from LiF (n=1.30 to 1.39) and theopposite substrate 18 is formed by a glass substrate (n=1.5), a materialhaving a refractive index of approximately 1.2 to 1.6 is preferably usedas the filling layer 17. For instance, Fluorinert that is inert liquidcontaining fluoride (n=1.30 to 1.39) is preferably used. Alternatively,polytetrafluoroethylene (n=136), polymethyl methacrylate (PMMA, n=1.49),or a film made from polymer containing fluoride (n=1.35 to 1.43) may beused.

The material for the filling layer 17 is not limited to the foregoingmaterial. Another material that has a refractive index that is almostthe same as or that is intermediate between those the low refractiveindex layer 16 and the opposite substrate 18 can be used. The lowerlimit of the refractive index can be approximately 1.2 or less since aneffect of providing the filling layer 17 can be achieved when therefractive index is larger than air (n=1).

The filling layer 17 can be formed by injecting liquid under a vacuumafter sealing a light-emitting element with the opposite substrate 18.Alternatively, the filling layer 17 can be manufactured by a dropletdischarging method, a dropping method, a printing method, a coatingmethod, or the like as typified by an ink jetting method.

The opposite substrate 18 is not limited to a glass substrate. A quartzsubstrate, various plastic substrates explained in Embodiment 1, or thelike can be used as the opposite substrate 18. The opposite substrate 18may be the same kind of a substrate 10. The other structure of thelight-emitting element according to this embodiment can be referred toEmbodiment 1.

Because the space between the low refractive index layer 16 and theopposite substrate 18 is filled with the filling layer 17 in thelight-emitting element according to the present invention, difference inrefractive indexes of an interface between the low refractive indexlayer 16 and the filling layer 17, and an interface between the fillinglayer 17 and the opposite substrate 18 can be reduced. Accordingly,light extraction efficiency can be further improved.

A light-emitting element according to the present invention can beadopted in a light-emitting device as typified by an EL display. Thelight-emitting device can be broadly divided into two kinds, that is, asimple matrix system in which an electroluminescent layer is formedbetween two kinds of stripe-shaped electrodes provided so as to be rightangles with each other, and an active matrix system in which anelectroluminescent layer is formed between a pixel electrode and anopposite electrode arranged in a matrix configuration and connected toTFT. The light-emitting element according to the present invention canbe applied to either of the simple matrix system and the active matrixsystem.

Embodiment 4

In this embodiment, the case of providing a stress relieving layer to abottom (pixel electrode side) of a passivation film is explained withreference to FIGS. 3A and 3B. In the foregoing embodiment, the stressrelieving layer is provided over the passivation film. Alternatively,peeling or cracking can be effectively prevented by forming a stressrelieving layer 15 a at the bottom of a passivation film 14 (FIG. 3A).By providing the stress relieving layer 15 a, the thickness of thepassivation film 14 can be increased without being adversely affected bypeeling or cracking of the passivation film 14. As a result, extremehigh blocking effects can be obtained. The stress relieving layer 15 amay have a lamination layer structure.

As the stress relieving layer 15 a, an organic material or inorganicmaterial having small stress may be appropriately used. For instance,SiNO is preferably used as the stress relieving layer. Alternatively,SiO or SiON can be used. Further alternatively, aromatic amines that iscategorized as a so-called hole transporting or injecting material in anEL element such as α-NPD (that may be referred to as simply NPD), NPD(4,4′-bis-[N-(naphtyl)-N-phenyl-amino]biphenyl) or TPD. In thisembodiment, the refractive index of the stress relieving layer 15 a isnot especially limited, and so a material for the stress relieving layercan be freely selected.

As illustrated in FIG. 3B, the stress relieving layer 15 a (first stressrelieving layer) and the stress relieving layer 15 b (second stressrelieving layer) can be provided so as to interpose the passivation film14 therebetween. Here, the stress relieving layer 15 b having thecondition described in Embodiment 1 may be used. On the other hand, thestress relieving layer 15 a is not especially limited. The foregoingmaterial may be selected to be used as the stress relieving layer 15 a.The materials for the stress relieving layers 15 a and 15 b may be thesame or different.

In the case that the passivation film 14 is interposed between thestress relieving layers, light extraction efficiency can be improvedwhile preventing peeling or cracking of the passivation film 14.

EXAMPLE 1

In this example, the structure of an active matrix display device (alsoreferred to as an active matrix light-emitting device) using alight-emitting element according to Embodiments 1 to 3 is explained withreference to FIGS. 4 and 5. A display device according to this examplehas a plurality of pixels 310 including a plurality of elements in aregion formed by the intersection of a source line Sx (x is a naturalnumber, 1≦x≦m) with a gate line Gy (y is a natural number, 1≦x≦n) via aninsulator (FIG. 4A). The pixel 310 has two transistors of alight-emitting element 313 and a capacitor element 316. Among the twotransistors, one is a transistor for switching 311 that controls inputof a video signal, and the other is a transistor for driving 312 thatcontrols ON/OFF of light of the light-emitting element 313. Thecapacitor element 316 serves to hold gate-source voltage of thetransistor 312.

A gate electrode of the transistor 311 is connected to the gate line Gy.One of a source electrode and a drain electrode is connected to thesource line Sx, and the other is connected to a gate electrode of thetransistor 312. One of a source electrode and a drain electrode of thetransistor 312 is connected to a first power source 317 via a powersource line Vx (x is a natural number, 1≦x≦1), and the other isconnected to a pixel electrode of the light-emitting element 313. Anopposite electrode (transparent electrode 13) is connected to a secondpower source 318. The capacitor element 316 is provided between the gateelectrode and the source electrode of the transistor 312. Thetransistors 311 and 312 may have either conductivity of n-type orp-type. FIG. 4 illustrates the structure in which the transistor 311 isan n-type and the transistor 312 is a p-type. The electric potential ofthe first power source 317 and the second power source 318 is notespecially restricted. The first power source 317 and the second powersource 318 are provided different electric potential from each other sothat forward bias voltage or reverse bias voltage is applied to thelight-emitting element 313.

A semiconductor constituting the transistors 311 and 312 may be anamorphous semiconductor (amorphous silicon), a microcrystallinesemiconductor, a crystalline semiconductor, an organic semiconductor, orthe like. The microcrystalline semiconductor may be formed by usingsilane gas (SiH₄) and fluorine gas (F₂), or silane gas (SiH₄) andhydrogen gas. Alternatively, the microcrystalline semiconductor may beformed by forming a thin film by using the foregoing gas and emittinglaser light to the thin film. The gate electrodes of the transistors 311and 312 are formed by a single layer or a laminated layer by aconductive material. For instance, the laminated layer is preferablyformed to have any one of the following structures; a lamination layerstructure formed by stacking tungsten (W) over tungsten nitride (WN), alamination layer structure formed by stacking aluminum (Al) andmolybdenum (Mo) over molybdenum (Mo), and a lamination layer structureformed by stacking molybdenum (Mo) over molybdenum nitride (MoN).

FIG. 4B is a top view of a display panel of a display device accordingto this example. In FIG. 4B, a display region 400 having a plurality ofpixels (pixels 310 illustrated in FIG. 4A) including light-emittingelements, gate drivers 401 and 402, a source driver 403, and aconnecting film 407 such as an FPC are formed over a substrate 405 (FIG.4B). The connecting film 407 is connected to an IC film or the like.

FIGS. 5A and 5B are cross-sectional views of a display panel illustratedin FIG. 4B taken along line A-B. FIG. 5A illustrates a top emissiondisplay panel, whereas FIG. 5B illustrates a dual emission displaypanel.

FIGS. 5A and 5B illustrate the transistor 312 (the transistor 311 inFIG. 4A is omitted) provided to the display region 400, thelight-emitting element 313, and an element group 410 provided to thesource driver 403. Reference numeral 316 denotes a capacitor element. Asealing agent 408 is provided around the periphery of the display region400, the gate drivers 401 and 402, and the source driver 403.Accordingly, the light-emitting element 313 is sealed with the sealingagent 408 and an opposite substrate 406. The sealing process is theprocess for protecting the light-emitting element 313 against moisture,in which case a cover material (glass, ceramic, plastic, metal, and thelike) is used for the sealing process. Alternatively, thermosettingresin or ultraviolet curing resin can be used for the sealing process,further alternatively, a thin film having high barrier property such asa metal oxide or nitride can be used. A material that has low refractiveindex with respect to air or a filing layer 17 described in Embodiment 3in order to improve light extraction efficiency.

As the sealing agent 408, ultraviolet curing or thermosetting epoxyresin may be used. Ultraviolet epoxy resin (2500 Clear manufactured byElectrolite Cooporation) having high resistance, a refractive index of1.50, viscosity of 500 cps, shore D hardness of 90, tensile intensity of3000 psi, Tg point of 150° C., volume resistance of 1×10¹⁵ Ω·cm,resistance voltage 450 V/mil.

In the light-emitting element 313, the transparent electrode 13 isconnected to the second power source 318 in FIG. 4A. An element formedover the substrate 405 is preferably made from a crystallinesemiconductor (polysilicon) having better characteristics such asmobility than that of an amorphous semiconductor. In this instance, itcan be realized that the surface of the panel becomes monolithic. Apanel having the foregoing structure can be reduced its size, weight,and thickness since the number of external ICs to be connected isreduced.

The display region 400 can be composed of a transistor having anamorphous semiconductor (amorphous silicon) formed over an insulatingsurface as a channel portion. The gate drivers 401 and 402, and thesource driver 403 can be composed of IC chips. The IC chips can bepasted onto the substrate 405 by a COG method or pasted onto theconnecting film 407 for connecting to the substrate 405. The amorphoussemiconductor can be readily formed over a large substrate by using aplasma CVD method. Further, a panel can be provided at low cost since aprocess of crystallization is not required. When a conductive layer isformed by a droplet discharging method as typified by an ink jettingmethod, the panel can be provided at further low cost.

FIG. 5A is explained in detail. In the structure illustrated in FIG. 5A,first, second, and third interlayer insulating films 411, 412, and 413are formed over the transistor 312 and the element group 410. Further, awiring 414 is formed via an opening portion that is provided in thefirst and second interlayer insulating films 411 and 412. The wiring 414serves as a source wiring or a drain wiring of the transistor 312 andthe element group 410, a capacitor wiring of the capacitor element 316,or the like. As the wiring 414, alloys containing aluminum and nickelare desirably used. The alloys can contain carbon, cobalt, iron,silicon, and the like. The rate of content of the foregoing materials inthe alloys are preferably from 0.1 to 3.0 atomic % of carbon; from 0.5to 7.0 atomic % of at least one element of nickel, cobalt, iron; andfrom 0.5 to 2.0 atomic % of silicon. These materials have thecharacteristic of having a low resistance value.

In the case that Al is used as the wiring 414, there is a problem ofgenerating corrosion of a pixel electrode 11, for example, ITO. Despiteof the problem, the wiring 414 can make good contact to ITO by forming alamination layer structure of interposing the Al (or Al—Si alloy)between Ti or TiN. For example, a lamination layer structure of stackingsequentially Ti, Al, and Ti over a substrate may be adopted. On theother hand, the foregoing Al—Si alloy, Al—C—Ni alloy, or the like hasoxidation-reduction potential that is about equal to that of atransparent conductive film such as ITO, and so the Al—Si alloy or theAl—C—Ni alloy can make direct contact to ITO or the like without havinga lamination layer structure (that is, being interposed between Ti, TiN,and the like). The wiring 414 can be formed by using a target formed bythe foregoing alloys by a sputtering method. In the case that etching isperformed by using resist as a mask, a wet etching method is preferablyused, in which case phosphoric acid or the like can be used as etchant.The wiring connected to the second power source 318 can be formed in thesame manner as that of the wiring 414.

The pixel electrode 11 is formed via an opening portion provided to thethird interlayer insulating film 413. A reflective conductive film isused as the pixel electrode 11 since the panel illustrated in FIG. 5A isa top emission panel.

The materials of the first to third interlayer insulating films are notespecially restricted. For instance, the first interlayer insulatingfilm may be made from an inorganic material, and the second and thirdinterlayer insulating films may be made from organic materials, in whichcase a film including carbon such as silicon oxide, silicon nitride,silicon oxynitride, DLC, or carbon nitride; PSG (phosphorus glass); BPSG(boron phosphorus glass); an alumina film; or the like can be used asthe inorganic material. As a method for forming, a plasma CVD method, alow pressure CVD (LPCVD) method, an atmospheric plasma method, or thelike can be used. Alternatively, an SOG film (for example, an SiOx filmincluding an alkyl group) formed by a coating method can be used.

As the organic material, a photosensitive or non photosensitive organicmaterial such as polyimide, acrylic, polyamide, resist, orbenzocyclobutene; or heat-resisting organic resin such as siloxane canbe used. As a method for forming the interlayer insulating films, a spincoating method, a dipping method, a spray coating method, dropletdischarging method (ink jetting method, screen printing method, offsetprinting method), a doctor knife, a roll coater, a curtain coater, knifecoater, or the like can be used. The first to third interlayerinsulating films can be formed by stacking the foregoing materials.

A bank layer 409 (also referred to as bank) is formed around theperiphery of the pixel electrode 11. As the bank layer 409, aphotosensitive or non photosensitive organic material such as polyimide,acrylic, polyamide, resist, or benzocyclobutene; or heat-resistingorganic resin such as siloxane; an inorganic insulating material (SiN,SiO, SiON, SiNO, or the like); or a lamination layer formed by theforegoing materials can be used. In this instance, photosensitiveorganic resin covered by a silicon nitride film is used. As theforegoing insulator, either a negative type photosensitive resin thatbecomes insoluble to etchant by light or a positive type photosensitiveresin that becomes dissoluble to etchant by light can be used.

The shape of a side of the bank layer 409 is not especially restricted.The bank layer 409 has preferably an S shape as illustrated in FIGS. 5Aand 5B or the like. In other word, the bank layer 409 has preferably aninfection point at the side face of the bank layer 409. Accordingly, thecoverage of an electroluminescent layer 12, a transparent electrode 13,and the like can be improved. The present invention is not limited tothe foregoing shape; the insulator may be formed to have a curved upperedge portion having a radius of curvature.

In such a way of Embodiments 1 to 3, the electroluminescent layer 12,the transparent electrode 13, a passivation film 14, a stress relievingfilm 15, a low refractive index layer 16, and the like are formed overthe pixel electrode 11. The illustrated structure utilizes, but notexclusively, Embodiment 1. For example, the filling layer 17 describedin Embodiment 3 may be provided in space 415. The upper layers over thepassivation film 14 are, but not exclusively, formed over the wholesurface of the substrate.

Since the third interlayer insulating film 413 is formed over the secondinterlayer insulating film 412 and the pixel electrode 11 is formedthereover in the structure illustrated in FIG. 5A, the design freedom ofthe structure is increased without being a region provided with thelight-emitting element 313 limited by a region provided with thetransistor 312 and the wiring 414. Accordingly, a display device havinga desired opening ratio can be obtained.

FIG. 5B is further explained in detail. In the structure illustrated inFIG. 5B, the first interlayer insulating film 411 and the secondinterlayer insulating film 412 are formed over the transistor 312 andthe element group 410. The wiring 414 is formed via an opening portionprovided to the first interlayer insulating film 411 and the secondinterlayer insulating film 412. The wiring 414 serves as a source wiringor a drain wiring of the transistor 312 and the element group 410, acapacitor wiring of the capacitor element 316, or the like. Thetransistor 312 is connected to the pixel electrode 14 via at least onewiring 141. FIG. 5B illustrates a dual emission type, and so atransparent conductive film is used as the pixel electrode 11. In theillustrated structure, the pixel electrode 11 is formed after formingthe wiring 414. However, the structure may be formed reversely.Alternatively, the wiring 414 and the pixel electrode 11 can be formedby one layer.

In this example, the first interlayer insulating film 411 formed overthe transistor 312 has a barrier property for preventing impurities suchas Na, O₂, or moisture from penetrating into the transistor 312 (thefirst interlayer insulating film may be referred to as a cap insulatingfilm by having the foregoing property), and so the first interlayerinsulating film is preferably formed as much as possible. Alternatively,the first interlayer insulating film can be omitted.

The bank layer 409 (also referred to as a bank) is formed around theperiphery of the pixel electrode 11. In such a way of Embodiments 1 to3, the electroluminescent layer 12, the transparent electrode 13, thepassivation film 14, the stress relieving film 15, the low refractiveindex layer 16, and the like are formed over the pixel electrode 11. Theillustrated structure utilizes, but not exclusively, Embodiment 1. Forexample, the filling layer 17 described in Embodiment 13 may be providedin space 415.

The light-emitting element according to the present invention is a topemission type (or a dual emission type) which emits light passingthrough the transparent electrode 13. For example, in the case that thetransparent electrode 13 serves as a cathode, an aluminum film having athickness of 1 to 10 nm or an aluminum film containing slightly Li maybe used for the transparent electrode 13. When using an aluminum film asthe transparent electrode 13, a material being contact with theelectroluminescent layer 12 can be formed by a material except an oxide,and so the reliability of a light-emitting device can be improved.Before forming the aluminum film having a thickness of 1 to 10 nm, alayer having a light-transmitting property (thickness of 1 to 5 nm) madefrom CaF₂, MgF₂, or BaF₂ may be formed as a cathode buffer layer. Inorder to reduce the resistance of the cathode, the transparent electrode13 may be formed to have a lamination layer structure composed of a thinmetal film having a thickness of 1 to 10 nm and a transparent conductivefilm (ITO, indium oxide-zinc oxide alloy (In₂O₃—ZnO), zinc oxide (ZnO),or the like). Alternatively, in order to reduce the resistance of thecathode, an auxiliary electrode may be provided over the transparentelectrode 13 in a region that is not to be an emission region. Thecathode may be formed selectively by using a resistance heating methodby vapor deposition with an evaporation mask.

A material and a structure of the first and second interlayer insulatingfilms, the wiring 414, the bank layer 409, and the like can be referredto the invention according to FIG. 5A.

In FIG. 5B, the pixel electrode 11 extends to a region provided with thecapacitor element 404, and serves as a capacitor electrode of thecapacitor element 404. The position of the connecting film 407 is overthe second interlayer insulating film 412, which is different from thatin FIG. 5A. The connecting film 407 and the element group 410 areconnected to each other via the wiring 414. Therefore, a dual emissiondisplay device can be obtained.

Each characterizing portion in the invention related to FIGS. 5A and 5Bcan be implemented by replacing or combining with each other. Thepresent invention can be freely combined with Embodiments and the otherExamples.

EXAMPLE 2

In this example, another structure of an active matrix display deviceaccording to Example 1 is explained with reference to FIGS. 6A and 6B.In a display device according to this example, color filters areprovided in each pixel portion, and at least one layer or a part of thelayer among the second and third interlayer insulating films and thebank layer 409 in Example 1 is doped with carbon or metal particleshaving a light-shielding property. Hereinafter, a detail descriptionwill be given.

A top emission display device has color filters 90 to 92 of R, G, and Bover an opposing substrate 406. The color filters 90 to 92 can be madefrom a known material by a known method. As a material for anelectroluminescent layer, a material that can exhibit white emission isbasically used. As the second interlayer insulating film and the banklayer, an interlayer insulating film 417 and a bank layer 416 having alight-shielding property formed by doping carbon or metal particles toan organic material such as acrylic, polyimide, or siloxane are used,respectively. On the other hand, the third interlayer insulating film413 is formed by using transparent organic resin such as acrylic,polyamide, or siloxane.

The interlayer insulating film 417 having a light-shielding property andthe bank layer 409 having a light-shielding property are formed in sucha way that carbon and metal particles having a light-shielding propertyare doped to an organic material such as acrylic, polyimide, orsiloxane, and the material is agitated by using a shaker or anultrasonic shaker, then, the agitated material is filtrated according toneed, and then, the foregoing interlayer insulating film 417 and banklayer 409 are formed by a spin coating. When doping carbon particles ormetal particles to an organic material, a surface active agent, adispersing agent, or the like may be doped to the organic material inorder that these particles are mixed thereinto uniformly. In the casethat the carbon particles are doped, the amount of doping the carbonparticles may be controlled so that the density of the carbon particlesis 5 to 15% by weight. Further, the thin film formed by a spin coatingwithout modification can be used as the interlayer insulating film 417and bank layer 409. Alternatively, the thin film can be baked to behardened. The transmittance of the deposited thin film is 0% or almost0%. The reflectance of the deposited thin film is 0% or almost 0%.

The interlayer insulating film 417 having a light-shielding property ofthe bank layer 416 having a light-shielding property may include partlya transparent insulating layer. On the other hand, the third interlayerinsulating film may include partly an insulating layer having alight-shielding property. In such a way of Embodiments 1 to 3, anelectroluminescent layer 12, a transparent electrode 13, a passivationfilm 14, a stress relieving film 15, a low refractive index layer 16,and the like are formed over a pixel electrode 11. The illustratedstructure utilizes, but not exclusively, Embodiment 1. For example, thefilling layer 17 described in Embodiment 3 may be provided in space 415.A material and a structure of the first interlayer insulating film 411and the wiring 414 can be referred to Example 1.

A top emission display device illustrated in FIG. 6A can preventboundaries between pixels from blurring due to the influence ofunnecessary light (including light generated by being reflected by abottom surface) emitted from a light-emitting layer by virtue of havingthe interlayer insulating film 417 having a light-shielding property andthe bank layer 416 having a light-shielding property. That is,boundaries between pixels become clear since the foregoing insulatingfilm having a light-shielding property absorbs the unnecessary light,and so a high-resolution image can be displayed. Since the influence ofunnecessary light can be prevented by a light-shielding film, apolarizing plate is made redundant, and the display device can bereduced its size, weight, and thickness. Further, unnecessary light canbe prevented from leaking into a transistor formation region of a pixel,and so active matrix driving can be possible by a transistor with highreliability.

In a dual emission display device illustrated in FIG. 6B, a transistor312 and a first interlayer insulating film 411 are formed over asubstrate 405, moreover, a first interlayer insulating film 417 having alight-shielding property is formed over the substrate 405. Openingportions for passing light generated in the light-emitting layer areprovided to the first interlayer insulating film 417 having alight-shielding property, and resin having a light-transmitting propertyand including pigment of R, G, and B is filled to the opening portions.Accordingly, color filters 93 to 95 are formed. The resin including thepigment is preferably formed by a droplet discharging methodselectively. Moreover, an opposite substrate 406 is provided with colorfilters 90 to 92 of R, G, and B as is the case with FIG. 6A. The colorfilters 90 to 92 can be formed by a known material and a known method.

As a part of the second interlayer insulating film or the bank layer,the interlayer insulating film 417 having a light-shielding property andthe bank layer 416 having a light-shielding property formed by dopingcarbon or metal particles to an organic material such as acrylic,polyimide, or siloxane are used. A part of the other portion of the banklayer 406 is formed by a transparent organic material such as acrylic,polyimide, or siloxane. The interlayer insulating film 417 having alight-shielding property may include partly a transparent insulatinglayer.

The interlayer insulating film 417 having a light-shielding property andthe bank layer 416 having a light-shielding property are formed in sucha way that carbon and metal particles having a light-shielding propertyare doped to an organic material such as acrylic, polyimide, orsiloxane, and the material is agitated by using a shaker or anultrasonic shaker, then, the agitated material is filtrated according toneed to be spin-coated into the foregoing interlayer insulating film 417and bank layer 409. When doping carbon particles or metal particles toan organic material, a surface active agent, a dispersing agent, or thelike may be doped to the organic material in order that these particlesare mixed thereinto uniformly. In the case that the carbon particles aredoped, the amount of doping the carbon particles may be controlled sothat the density of the carbon particles is 5 to 15% by weight. Further,the thin film formed by a spin coating without modification can be usedas the interlayer insulating film 417 and bank layer 409. Alternatively,the thin film can be baked to be hardened. The transmittance of thedeposited thin film is 0% or almost 0%. The reflectance of the depositedthin film is 0% or almost 0%.

In such a way of Embodiments 1 to 3, the electroluminescent layer 12,the transparent electrode 13, the passivation film 14, the stressrelieving film 15, the low refractive index layer 16, and the like areformed over the pixel electrode 11. The illustrated structure utilizes,but not exclusively, Embodiment 1. For example, the filling layer 17described in Embodiment 3 may be provided in space 415. A material and astructure of the first interlayer insulating film 411 and the wiring 414can be referred to Example 1.

A dual emission display device illustrated in FIG. 6B can preventboundaries between pixels from blurring due to the influence ofunnecessary light (including light generated by being reflected by abottom surface) emitted from a light-emitting layer by virtue of havingthe interlayer insulating film 417 having a light-shielding property andthe bank layer 416 having a light-shielding property. That is,boundaries between pixels become clear since the foregoing insulatingfilm having a light-shielding property absorbs the unnecessary light,and so a high-resolution image can be displayed. Since the influence ofunnecessary light can be prevented by a light-shielding film, apolarizing plate is made redundant, and the display device can bereduced its size, weight, and thickness. Further, unnecessary light canbe prevented from leaking into a transistor formation region of a pixel,and so active matrix driving can be possible by a transistor with highreliability.

In the case of forming a color filter, a black matrix (a lattice-shapedor stripe light-shielding film for separating each pixel of R, G, and Boptically) is generally provided. However, the interlayer insulatingfilm 417 having a light-shielding property and the bank layer 416 havinga light-shielding property are formed corresponding to a region thatshould be provided with the black matrix in the invention according tothe structure illustrated in FIGS. 6A and 613. Therefore, manufacturingyields are improved since alignment can be readily carried out, and thecost can be reduced since an extra process is not required to be added.

In this example, the display panel can exert the foregoing effect suchas preventing adverse affects due to unnecessary light generated in alight-emitting layer in the case that at least either of the interlayerinsulating film 417 having a light-shielding property and the bank layer416 having a light-shielding property is formed. Needless to way, bothof the foregoing layers are preferably formed. Each characterizingportion in the invention related to FIGS. 6A and 6B can be implementedby replacing or combining with each other. The present invention can befreely combined with Embodiments and the other Examples.

EXAMPLE 3

An example of a structure of a light-emitting element according toEmbodiments is explained in this example. As a sample for reference, anEL element for reference is manufactured to have a laminated layerstructure by stacking sequentially over a substrate an anode ITO (110nm), α-NPD (40 nm), Alq₃: DMQd (quinacridone derivative) (37.5 nm), Alq₃(20 nm), BzOS: Li (20 nm), and a cathode ITO (110 nm). Moreover, an ELelement is manufactured by forming layers listed in Table 1 (the ELelement has the structure in which a passivation film is interposedbetween stress relieving layers in this example) over the cathode ITO tomeasure luminance of light emitted to the top direction at appliedcurrent having current density of 2.5 mA/cm². Luminance (105.8 cd/m²) ofthe reference EL element measured at applied current having currentdensity of 2.5 mA/cm² is compared to that of the foregoing EL element.As a result, the luminance listed in Table 1 is increased than that ofthe reference EL element.

TABLE 1 Laminated Structure over Cathode ITO Upper Surface-sideIncreasing Ratio of 1st Stress Passivation 2nd Stress Low RefractiveLuminance at Luminance Compared Relieving Film Film Relieving Film IndexLayer 2.5 mA/cm² (cd/m²) to Reference SiNO (50 nm) SiN (150 nm) SiNO (20nm) MgF₂ (10 nm) LiF (10 nm) 133 26%  SiNO (50 nm) SiN (150 nm) NPD (20nm) MgF₂ (10 nm) LiF (10 nm) 106.7 1% NPB (50 nm) SiN (150 nm) NPD (20nm) MgF₂ (10 nm) LiF (10 nm) 107 1%

The foregoing measurement results show that SiNO is preferably used asthe stress relieving layer among others. The reference EL element hasnot so good reliability since dark spots are generated therein, whereasthe EL element having the lamination layer structure listed in Table 2has good reliability since dark spots are drastically reduced or darkspots are not observed therein. Needless to say, peeling or crack of theSiN layer serving as a passivation film is not occurred because of thestress relieving film.

In another embodiment or example, a stress relieving layer can be newlyformed between the transparent electrode 13 and the passivation film. Amaterial for the stress relieving layer may be the same or different ofthe stress relieving material formed over the passivation film.

EXAMPLE 4

In this example, an example of method for manufacturing a passivationfilm 14 and a stress relieving layer 15 according to the presentinvention is explained. Firstly, the passivation film 14 can be formedby a single layer or a lamination layer of a silicon nitride film, asilicon oxide film, silicon oxynitride film, a DLC film, a CN film by asputtering method or a CVD method. Especially, the passivation film 14is preferably formed by a silicon nitride film deposited by aradio-frequency sputtering method using a silicon target. A fine siliconnitride film obtained by the RF sputtering method using a silicon targetcan prevent an active element such as a TFT (thin film transistor) frombeing contaminated by alkali metal such as natrium, lithium, ormagnesium or alkali earth metal to prevent effectively the variation ofa threshold value. In addition, the fine silicon nitride film has anextreme high blocking effect against moisture or oxygen. In order toincrease a blocking effect, oxygen and hydrogen contents in the siliconnitride film may be preferably 10 atomic % or less, preferably, 1 atomic% or less.

As a specific sputtering condition, a nitride gas or a mixed gas ofnitrogen and rare gas, pressure of 0.1 to 1.5 Pa, frequency of 13 to 40MHz, electric power of 5 to 20 W/cm², substrate temperature of roomtemperature to 350° C., distance between silicon target (1 to 10 Ωcm)and a substrate of 40 to 200 mm, and back pressure of 1×10⁻³ Pa or less.Heated rare gas may be sprayed to the back of a substrate. For example,a fine silicon nitride film has characteristics that it has a slowetching rate (hereinafter, the etching rate refers to a rate of etchingat 20° C. by using LAL 500) of 9 nm or less (preferably, 0.5 to 3.5 orless), and low hydrogen density of 1×10²¹ atoms/cm⁻³ or less. The finesilicon nitride film is obtained under the condition, that is, flowratio of Ar:N₂=20 sccm:20 sccm, pressure of 0.8 Pa, frequency of 13.56MHz, electric power of 16.5 W/cm², substrate temperature of 200° C.,distance between a silicon target and a substrate of 60 mm, and backpressure of 3×10⁻⁵ Pa. The LAL500 is high-purity buffered hydrogenfluoride LAL500 SA grade manufactured by STELLA CHEMIFA CORPORATION thatis solution of NH₄HF₂ (7.13%) and NH₄F (15.4%).

The foregoing silicon nitride film obtained by a sputtering method has adielectric constant of 7.02 to 93, a refractive index of 1.91 to 2.13,an internal stress of 4.17×10⁸ dyn/cm², an etching rate of 0.77 to 1.31nm/min. A positive sign and a minus sign of the internal stress arechanged with each other depending on a compression stress and a tensilestress, in which case only an absolute value is mentioned. The foregoingsilicon nitride film obtained by a sputtering method has Si density of37.3 atomic % and N density of 55.9% that are measured by RBS. Theforegoing silicon nitride film obtained by a sputtering method hashydrogen density of 4×10²⁰ atoms/cm⁻³, oxygen density of 8×10²⁰atoms/cm⁻³, and carbon density of 1×10¹⁹ atoms/cm⁻³ that are measured bySIMS. The foregoing silicon nitride film obtained by a sputtering methodhas transmittance of 80% or more in a visible light region.

In each of the foregoing structure, the thin film having carbon as itsmain component is the DLC film, the CN film, or the amorphous carbonfilm in a thickness of 3 to 50 m. The DLC film has a SP³ bond as thecarbon-carbon bond as short range order; however, the DLC film has anamorphous structure macroscopically. The DLC film is composed of carbonof 70 to 95 atomic % and hydrogen of 5 to 30 atomic %.

The DLC film is so hard and provides excellent electrical isolation. Inaddition, the DLC film is stable chemically and hardly transforms.Further, the DLC film has thermal conductivity of 200 to 600 W/m·K and arefractive index of 2.3 to 2.3, and can release heat generated indriving. Such the DLC film has a characteristic of having lowpermeability of gas such as water vapor or oxygen. It is known that theDLC film has hardness of 15 to 25 GPa measured by micro hardness tester.

The DLC film can be formed by a plasma CVD method (typically, an RFplasma CVD method, a microwave CVD method, an electron cyclotronresonance (ECR) CVD method, a thermal filament method CVD method), acombustion method, a sputtering method, an ion beam vapor depositionmethod, a laser vapor deposition method, or the like. The DLC film canbe formed with good adhesiveness with any method. The DLC film is formedby setting a substrate to a cathode. Alternatively, a hard film can beformed by applying negative bias to utilize ion bombardment to someextent. As a reaction gas used for depositing the DLC film, a hydrogengas and a gas made from carbon hydride (for example, CH₄, C₂H₂, or C₆H₆)are used. The gas is ionized by glow discharge to yield acceleratedcollision of ions against the cathode applied with negative self bias.Accordingly, a fine and smooth DLC film can be obtained. Further, theDLC film is transparent or semitransparent to visible light. As usedherein, the term “transparent to visible light” refers to transmittanceof visible light of 80 to 100%, whereas the term “semitransparent tovisible light” refers to transmittance of visible light of 50 to 80%.

As a reaction gas used for depositing the CN film, a nitrogen gas and agas made from carbon hydride (for example, C₂H₂ or C₂H₄) may be used.

Then, a stress relieving layer 15 is explained. The stress relievinglayer is formed by an alloy film such as MgO, SrO₂, SiO, or CaN; or amaterial film including an organic compound such as α-NPD(4,4′-bis-[N-(naphtyl)-N-phenyl-amino]biphenyl), BCP (bathocuproin),MTDATA (4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine),Alq₃ (tris-8-quinolinolatoaluminum complex). As noted above, the stressrelieving film can be formed by the same material as that of at leastone layer among a plurality of layers that constitutes a layercontaining an organic compound (electroluminescent layer) interposedbetween an anode and a cathode. The stress relieving layer may be a highmolecular material film containing an organic compound obtained by acoating method (an ink jetting method or a spin coating method). Forexample, the foregoing material is preferably used for the stressrelieving film not only for its low film stress and its transparency,but for its hygroscopicity.

EXAMPLE 5

Another structure of an active matrix display device according toExample 1 is explained with reference to FIGS. 7A and 7B. An activematrix display device illustrated in FIG. 7A comprises a low refractiveindex layer 418 formed over both faces or at least one face of anopposite substrate 406. As the low refractive index layer 418, lithiumfluoride (LiF, n=1.30 to 139), magnesium fluoride (MgF₂=1.38 to 1.40),barium fluoride (BaF₂, n=1.47), or the like having a refractive indexthat is higher than that of air and lower than that of the oppositesubstrate 406, typically, a glass substrate. Further, in the case thatthe low refractive index layer 418 is formed over both faces of anopposite substrate 406, the materials for the low refractive index layer418 over both faces may be the same or different.

An opposite substrate that is formed by depositing LiF over bothsurfaces of a glass substrate to have a thickness of 30 nm as the lowrefractive index layer 418 is used to manufacture an EL element of 1×1.Measurement of the luminance of the EL element at current density of 2.5mA/cm² can show approximately 3% of increased luminance despite of thethickness of a cathode (transparent electrode 13).

Each transmittance of the following opposite substrates is measured,that is, 1) an opposite substrate formed by glass, 2) an oppositesubstrate formed by stacking glass over a low refractive index layer, 3)an opposite substrate formed by stacking a low refractive index layerover glass, and 4) an opposite substrate formed by stacking glass and alow refractive index layer over a low refractive index layer. Thismeasurement yields that transmittance is improved in the number order,that is, luminance is increased in the number order.

An active matrix display device illustrated in FIG. 7B comprises a lowrefractive index layer 418 formed over both faces or at least one faceof an opposite substrate 406, and a filling layer 417 formed between alow refractive index layer 16 at the side of a light-emitting elementand the low refractive index layer formed over the opposite substrate406. As a material for the low refractive index layer, the same materialused in FIG. 7A can be used. The filling layer 17 has preferably arefractive index that is almost the same as that of refractive indexesof the low refractive index layer 16 and the low refractive index layer418 or that is intermediate between those of the low refractive indexlayer 16 and the low refractive index layer 418. For example, a filmmade from Fluorinert that is inert liquid containing fluorine (n=1.23 to1.31) is preferably used. Alternatively, polytetrafluoroethylene(n=1.36), polymethacrylic acid methyl (PMMA, n=1.49), polymer containingfluorine (n=1.35 to 1.43) can be used.

It is not limited to the foregoing material. Another material that has arefractive index that is almost the same value as those or anintermediate value of those of both the low refractive index layers canbe used. The lower limit of the refractive index may be approximately1.2 or less since an effect of providing the filling layer 17 can beachieved when the refractive index is larger than air (n=1). The fillinglayer 17 can be formed by injecting liquid in vacuum after sealing alight-emitting element with the opposite substrate 406. Alternatively,the filling layer 17 can be formed by a droplet discharging method, adropping method, a printing method, a coating method as typified by anink jetting method.

An active matrix type display device is explained in this example;however, a display device that has technical features of the inventionaccording to Examples 1 to 3 and has a structure in which a lowrefractive layer is provided to an opposite substrate can be alsoapplied to a passive matrix display device. Another constitution of thepresent invention illustrated in FIG. 7 is according to anotherembodiment or example. This example can be freely combined with theforegoing embodiment or another example.

EXAMPLE 6

In this example, an example of a pixel circuit that can be applied tothe present invention except the pixel circuit illustrated in FIG. 4A isexplained with reference to FIGS. 8A and 8B. FIG. 8A illustrates a pixelcircuit having a structure in which a transistor 340 for erasing and agate wiring Ry for erasing are newly provided in a pixel 310 illustratedin FIG. 4A. Since the pixel circuit can make forcibly a light-emittingelement 313 have the state of not being applied with current by thearrangement of the transistor 340, a lightning period can be startedsimultaneously with or immediately after starting a write period withoutwaiting write of signals into all of pixels 310. Therefore, a duty ratiois improved, and a moving image can be especially displayed well.

FIG. 8B illustrates a pixel circuit in which a transistor 312 of thepixel 310 illustrated in FIG. 4A is omitted and transistors 341, 342,and a power source line Vax (x is a natural number, 1≦x≦1) are newlyprovided. The power source line Vax is connected to a power source 343.In this structure, potential of a gate electrode of the transistor 341is fixed and the transistor 341 is operated in a saturation region byconnecting the gate electrode of the transistor 341 to the power sourceline Vax that maintains the potential of the gate electrode constant.Further, the transistor 342 is operated in a linear region and a videosignal including information of lightening and non-lightening of a pixelis inputted to the gate electrode of the transistor 342. Since the valueof source-drain voltage of the transistor 342 operating in a linearregion is small, slight variation of the source-drain voltage of thetransistor 342 does not affect the current value of the light-emittingelement 313. Therefore, the value of current passing through thelight-emitting element 313 is depending on the transistor 341 operatingin the saturation region. The present invention having the foregoingconstitution can improve luminance variation of the light-emittingelement 341 due to characteristic variation of the transistor 341 toimprove image quality. This example can be freely combined with theforegoing embodiment and another example.

EXAMPLE 7

In this example, laminated layer structures of a wiring 414 (the wiring414 includes a second power source 318 through this example) and a pixelelectrode 11 in the foregoing example are explained with reference toFIGS. 9A to 9D. Each diagram in FIGS. 9A to 9D illustrates an extractedportion of a light-emitting element of a pixel region. In the FIGS. 9Ato 9D, a passivation film, a stress relieving layer, a low refractiveindex, and the like are not illustrated.

FIG. 9A illustrates that the wiring is formed to have a laminated layerstructure of Mo 600 and an alloy 601 containing aluminum and the pixelelectrode 11 is formed by ITO 602. As the alloy 601 containing aluminum,aluminum containing carbon, nickel, cobalt, iron, silicon, and the likeis preferably used. The rate of content of the carbon is preferably 0.1to 3.0 atomic %; at least one kind of the nickel, the cobalt, and theiron, 0.5 to 7.0 atomic %; and the silicon, 0.5 to 2.0 atomic %. Thematerial has one characteristic of having low resistance of 3.0 to 5.0Ωcm. Here, the Mo 600 serves as barrier metal.

In the case that at least one kind of the nickel, the cobalt, and theiron is contained at 0.5% or more in the alloy 600 containing aluminum,the alloy 600 can be close to electrode potential of the ITO 602, and sothe alloy can make directly contact to the ITO 602. Further, heatresistance of the alloy 601 containing aluminum is increased. By settingthe rate of content of the carbon 0.1% or more, occurrence of hillockcan be prevented. There is an advantage that hillock is also preventedby mixing silicon into the alloy 600 or heating the alloy 600 at hightemperature.

FIG. 9B illustrates that an alloy 603 containing aluminum is used as awiring and the ITO 602 is used as a pixel electrode 11. Here, the alloy603 containing aluminum contains at least nickel. After forming thealloy 603 containing aluminum, nickel contained in the alloy seeps outto react chemically with silicon in a silicon semiconductor layer 608 ofan active element (for example, a TFT) for driving the pixel region.Accordingly, nickel silicide 607 is formed. There is an advantage ofimproving a conjugative property.

FIG. 9C illustrates that an alloy 604 containing aluminum is stacked asa wiring and ITO is stacked as a pixel electrode 11. It can be found byway of experiment that planarization is drastically improved especiallyin the case that a laminated layer structure of the alloy 604 containingaluminum and the ITO is adopted. For example, the planarization is twotimes as favorable as that of a laminated layer structure of a wiringformed by stacking TiN over an Al—Si alloy and ITO and a laminated layerstructure of a wiring formed by stacking TiN over an Al—Si alloy andITSO.

FIG. 9D illustrates that alloys 604 and 606 containing aluminum are usedas a wiring and a pixel electrode.

Since the alloy containing aluminum can be formed by patterning by a wetetching method, the alloy containing aluminum can be widely used notonly as a wiring or a pixel electrode. The alloy containing aluminum hashigh reflectivity, and so it is preferably used in a top emissiondisplay device. In the case of a dual emission display device, thewiring or the pixel electrode is required to be formed into a thin filmso as to pass light therethrough. This example can be freely combinedwith the foregoing embodiment or another example.

EXAMPLE 8

As an electric appliance using a display device including a pixel regionhaving a light-emitting element according to the present invention, atelevision device (TV, TV receiver), a camera such as a digital cameraor a digital video camera, a cellular phone device (cellular phone), apersonal digital assistant, a portable game machine, a monitor, acomputer, a sound reproduction device such as a car audio, an imagereproduction device having a recording medium such as a domestic gamemachine, and the like can be nominated. Specific examples are explainedwith reference to FIGS. 10A to 10F.

A personal digital assistant using a display device according to thepresent invention illustrated in FIG. 10A includes a main body 9201, adisplay device 9202, and the like and can display a high resolutionimage by the present invention. A digital camera using a display deviceaccording to the present invention illustrated in FIG. 10B includesdisplay portions 9701, 9702, and the like and can display a highresolution image by the present invention. A portable terminal using adisplay device according to the present invention illustrated in FIG.10C includes a main body 9101, a display portion 9102, and the like andcan display a high resolution image by the present invention. A portabletelevision device using a display device according to the presentinvention illustrated in FIG. 10D includes a main body 9301, a displayportion 9302, and the like and can display a high resolution image bythe present invention. A laptop personal computer using a display deviceaccording to the present invention illustrated in FIG. 10E includes amain body 9401, a display portion 9402, and the like and can display ahigh resolution image by the present invention. A television deviceusing a display device according to the present invention illustrated inFIG. 10F includes a main body 9501, a display portion 9502, and the likeand can display a high resolution image by the present invention. In thecase that an interlayer insulating film having a light-shieldingproperty and a bank layer having a light-shielding property areprovided, an influence due to unnecessary light can be suppressed, andso a polarizing plate is not required, which yields to reduce the size,the weight, and the thickness.

A brief explanation of the main structure of the foregoing televisiondevice is given with reference to a block diagram in FIG. 11. In FIG.11, an EL display panel 801 is manufactured by using a display deviceaccording to the present invention. A method for connecting the ELdisplay panel 801 to an external circuit are as follows; that is, 1) amethod of forming together a pixel portion of a display panel and ascanning line driver circuit 803 over a substrate and implementing asignal line driver circuit 802 separately as a driver IC, 2) a method offorming only a pixel portion of a display panel, and mounting thescanning driver circuit 803 and the signal line driver circuit 802thereto by a TAB system, 3) a method of mounting the scanning drivercircuit 803 and the signal line driver circuit 802 to the pixel portionof the display panel and the periphery thereof by a COG system. Any formcan be adopted.

Another structure of an external circuit at an input side of a videosignal comprises a video wave amplifier circuit 805 that amplifies avideo signal among signals received by a tuner 804, a video signalprocessing circuit 806 that converts the signal outputted from the videowave amplifier circuit 805 into a color signal corresponding to eachcolor of red, green, and blue, and a control circuit 807 that convertsthe video signal to input specification of the driver IC. In the case ofdigital driving, a signal dividing circuit 808 may be provided at asignal line side to divide an input digital signal into m numbers ofpieces to be supplied.

Among signals received by the tuner 804, a voice signal is transmittedto a voice wave amplifier circuit 809 and the output is supplied to aspeaker 813 via a voice signal processing circuit 810. A control circuit811 receives information on controlling a receiving station (receivedfrequency) or volume to send a signal to the tuner 804 and the voicesignal processing circuit 810.

A television set as illustrated in FIG. 10F can be completed byinstalling such the external circuit and the EL display panel into ahousing. Needless to say, the present invention is not limited to thetelevision set but can be applied to various usages especially as alarge display medium such as a monitor of a personal computer, aninformation board in the station or the airport, or an advertisementboard in the street. This example can be freely combined with theforegoing embodiment or another example.

EXAMPLE 9

A display device according to the present invention can be used as an IDcard capable of sending and receiving data out of touch by installing afunctional circuit such as a memory or a processing circuit or anantenna coil to the display device. An example of the structure of suchan ID card is explained with reference to drawings.

FIG. 12A illustrates one embodiment of an ID card installed with adisplay device according to the present invention. The ID cardillustrated in FIG. 12A is a non-contact type ID card that sends andreceives data to/from a reader/writer of a terminal device. Referencenumeral 101 denotes a card main body, and reference numeral 102 denotesa pixel portion of a display device installed to the card main body 101.

FIG. 12B illustrates the structure of a card substrate 103 included inthe card main body 101 illustrated in FIG. 12A. An ID chip 104 formed bya thin semiconductor film and a display device 105 according to theforegoing embodiment or example are pasted onto the card substrate 103.Both of the ID chip 104 and the display device 105 are formed over asubstrate prepared separately and transferred over the card substrate103. As a method of transferring, a thin film integrated circuit ismanufactured by a multiple of TFTs, and the thin film integrated circuitis pasted with a small vacuum tweezers, or selectively pasted by using aUV light irradiation method. A pixel portion or a driver circuit unit inthe display device can be transferred in accordance with the foregoingmethod. A portion that is formed by using a thin film semiconductor filmincluding the ID chip 104 and the display device 105 to be transferredis referred to as a thin film portion 107.

An integrated circuit 106 manufactured by using a TFT is mounted to thecard substrate 103. A method of mounting the integrated circuit 106 isnot especially restricted. A known COG method, a wire bonding method, aTAB method, and the like can be used. The integrated circuit 106 iselectrically connected to the thin film portion 107 via a wiring 108that is provided to the card substrate 103.

An antenna coil 109 electrically connected to the integrated circuit 106is formed over the card substrate 103. Since data can be sent andreceived by the antenna coil 109 by utilizing electromagnetic induction,a non-contact type ID card is less subject to damage due to physicalabrasion than a contact type ID card. The non-contact type ID card canbe used as a tag (wireless tag) that controls information out of touch.The non-contact type ID card can control so much larger amount ofinformation than that of a bar code that can also read information outof touch. The distance between the object and the terminal device thatcan read information can be made longer than that between the object andthe bar code.

FIG. 12B illustrates an example of forming the antenna coil 109 over thecard substrate 103; however, an antenna coil manufactured separately canbe mounted to the card substrate 103. For example, a copper wire or thelike is winded into a coil form to be pressed between two plastic filmshaving thicknesses of approximately 100 μm can be used as an antennacoil. Alternatively, an antenna coil can be formed into the thin filmintegrated circuit. The single antenna coil 109 is used in the single IDcard in FIG. 12B; however, a plurality of the antenna coils 109 can beused.

FIGS. 12A and 12B illustrate a mode of the ID card mounted with thedisplay device 105; however, the present invention is not limitedthereto, the display device is not always required to be provided. Inthe case of providing the display device, the data of a photograph ofthe face can be displayed on the display device, which can yielddifficulty in substitution of the photograph of the face compared to aprinting method. The display device can display information except thephotograph of the face, which can improve the function of the ID card.

As the card substrate 103, a plastic substrate having flexibility can beused. As the plastic substrate, ARTON made from norbornene resin havinga polar group manufactured by JSR Corporation can be used. Further, aplastic substrate such as polyethylene terephthalate (PET), polyethersulfone (PES), polyethylenenaphthalate (PEN), polycarbonate (PC), nylon,polyetheretherketone (PEEK), polysulfone (PSF), polyetherimide (PEI),polyarylate (PAR), polybutylene terephthalate (PBT), or polyimide can beused.

In this example, the electrical connection of an ID chip and a thin filmintegrated circuit is not limited to a mode illustrated in FIGS. 12A and12B. For example, a terminal of the ID chip can be directly connected toa terminal of the thin film integrated circuit by anisotropic conductiveresin or solder.

In FIG. 12, the thin film integrated circuit and the wiring provided tothe card substrate can be connected with each other by a wire bondingmethod, a flip chip method using a solder ball, or connected directlywith each other by using anisotropic conductive resin or solder. Thisexample can be freely combined to the foregoing embodiment or anotherexample. Further, the display device according to the present inventioncan be used by being built into a semiconductor device such as an IDtag, a wireless chip, or a wireless tag.

EXAMPLE 10

A light-emitting element according to the present invention as describedabove can be applied to a pixel portion of a light-emitting devicehaving a display function or a lightening portion of a light-emittingdevice having a lightening function. In this example, a circuitstructure and a driving method of the light-emitting device having adisplay function is explained with reference to FIGS. 13 to 16.

FIG. 13 is a schematic view of a top face of a light-emitting deviceapplied with the present invention. A pixel portion 6511, a sourcesignal line driver circuit 6512, a writing gate signal line drivercircuit 6513, and an erasing gate signal line driver circuit 6514 areprovided over a substrate 6500. Each of the source signal line drivercircuit 6512, the writing gate signal line driver circuit 6513, and theerasing gate signal line driver circuit 6514 is connected to an FPC(flexible printed circuit) 6503 that is an external input terminal via awiring group. Each of the source signal line driver circuit 6512, thewriting gate signal line driver circuit 6513, and the erasing gatesignal line driver circuit 6514 receives a video signal, a clock signal,a start signal, a reset signal, and the like from the FPC 6503. Aprinted wiring board (PWB) 6504 is fixed to the FPC 6503. The drivercircuit portion is not always required to be provided over a substrateso as to share the substrate with the pixel portion 6511. For example,the driver circuit portion may be formed at the outside of the substrateby using TCP or the like that is formed by mounting an IC chip over anFPC provided with a wiring pattern.

In the pixel portion 6511, a plurality of source signal line extended incolumns is arranged in rows. A current supply line is arranged in rows.In the pixel portion 6511, a plurality of gate signal lines extended inrows is arranged in columns. In the pixel portion 6511, a plurality ofpairs of circuits including a light-emitting element is arranged.

FIG. 14 is a diagram for showing a circuit for operating one pixel. Thecircuit illustrated in FIG. 14 comprises a first transistor 901, asecond transistor 902, and a light-emitting element 903. Each of thefirst transistor 901 and the second transistor 902 is a three-terminalelement including a gate electrode, a drain region, and a source region,in which a channel region is formed between the drain region and thesource region. Since the source region and the drain region are varieddepending on the structure of a transistor, an operational condition,and the like, it is difficult to distinguish the source region from thedrain region. In this example, regions serving as a source or a drainare referred to as a first electrode and a second electrode,respectively.

A gate signal line 911 and a writing gate signal line driver circuit 913are provided so as to be electrically connected or non-connected witheach other by a switch 918. The gate signal line 911 and an erasing gatesignal line driver circuit 914 are provided so as to be electricallyconnected or non-connected with each other by a switch 919. A sourcesignal line 912 is provided so as to electrically connect to either asource signal line driver circuit 915 or a power source 916 by a switch920. The gate of the first transistor 901 is electrically connected tothe gate signal line 911. The first electrode of the first transistor901 is electrically connected to the source signal line 912, and thesecond electrode of the first transistor 901 is electrically connectedto the gate electrode of the second transistor 902. The first electrodeof the second transistor 902 is electrically connected to the currentsupply line 917 and the second electrode of the second transistor 902 iselectrically connected to one electrode included in the light-emittingelement 903. The switch 918 may be included in the writing gate signalline driver circuit 913. The switch 919 may be included in the erasinggate signal line driver circuit 914. The switch 920 may be included inthe source signal line driver circuit 915.

The arrangement of a transistor, a light-emitting element, and the likein a pixel portion is not especially restricted. For example, theforegoing components can be arranged as shown in a top view of FIG. 15.In FIG. 15, the first electrode of a first transistor 1001 is connectedto a source signal line 1004, and the second electrode of the firsttransistor 1001 is connected to the gate electrode of the secondtransistor 1002. A first electrode of the second transistor is connectedto a current supply line 1005, and a second electrode of the secondtransistor is connected to an electrode 1006 of a light-emittingelement. A part of a gate signal line 1003 serves as a gate electrode ofthe first transistor 1001.

A method of driving is explained. FIG. 16 is an explanatory view of anoperation of a frame with time. In FIG. 16, a crosswise directionrepresents passage of time, whereas a lengthwise direction representsthe number of scanning stages of a gate signal line.

When an image is displayed by using a light-emitting device according tothe present invention, an operation of rewriting and an operation ofdisplaying are repeatedly carried out in a display period. The number ofrewriting is not especially restricted; however, the number of rewritingis preferably approximately 60 times for 1 second so that a person whowatches the image does not find flickering. The period in which theoperations of rewriting and displaying of one image (one frame) arecarried out is referred to as one frame period.

One frame is time-divided into four sub frames 501, 502, 503, and 504including write periods 501 a, 502 a, 503 a, and 504 a, and retentionperiods 501 b, 502 b, 503 b, and 504 b. A light-emitting element that isgiven signals for emitting light is in an emitting state in theretention period. A ratio of a length of the retention period in eachsub frame between a first sub frame 501, a second sub frame 502, a thirdsub frame 503, and a fourth sub frame 504 is the following:2³:2²:2¹:2⁰=8:4:2:1. Accordingly, a 4-bit gray scale can be offered. Thenumber of bits or scales is not limited thereto. For instance, an 8-bitgray scale can be offered by providing eight sub frames.

An operation in one frame is explained. Firstly, a writing operation iscarried out from the first line to the last line sequentially in the subframe 501. Therefore, the starting time of a write period is differentdepending on lines. Lines move to the retention period 501 b in theorder of finishing the write period 501 a. In the retention period, alight-emitting element that is given signals for emitting light is in anemitting state. Lines move to the next sub frame 502 in the order offinishing the retention period 501 b, and a writing operation is carriedout from the first line to the last line sequentially as is the casewith the sub frame 501. Operations as noted above are repeatedly carriedout to finish at last the retention period 504 b of the sub frame 504.When an operation in the sub frame 504 is finished, an operation in thenext frame is started. The integration of the time of emitting light ineach of the sub frames is an emitting time of each light-emittingelement in one frame. By varying the emitting time for eachlight-emitting element to be variously combined in one pixel, variousdisplaying color can be formed having different luminance andchromaticity.

In the case that write is finished before finishing the write of a lastline and a retention period in the line moved to a retention period isintended to be forced into termination as is the case with the sub frame504, an erase period 504 c is provided after the retention period 504 bto control so that a line is forced into a non-emission state. The lineforced into a non-emission state holds the state over a fixed period oftime (the period is referred to as a non-emission period 504 b). Uponfinishing the write period of the last line, lines move to the nextwrite period (or a frame) from the first line. As illustrated in FIG.18, one horizontal period is divided into two, either of which is usedto write and the other of which is used to erase, to write is carriedout in a pixel of a certain line and an input of an erasing signal formaking a pixel be a non-emission state is carried out in a pixel of acertain line. In the divided horizontal period, each gate signal line911 is selected to input a corresponding signal to a source signal line912. For instance, the former horizontal period selects the i line, andthe later horizontal period selects the j line in a certain horizontalperiod. Hence, it is possible to operate as if two lines are selectedsimultaneously. That is, a video signal is written into a pixel in writeperiods 501 a to 504 a by using a write period of each of one horizontalperiod, in which case a pixel is not selected in an erase period in onehorizontal period. A signal written into a pixel in the erase period 504c is erased by using an erase period in another horizontal period, inwhich case a pixel is not selected in a write period in one horizontalperiod. Therefore, a display device having a pixel with a high openingratio can be provided and manufacturing yields can be improved.

In this example, the sub frames 501 to 504 are arranged in the order ofdescending retention period; however, the present invention is notlimited thereto. For instance, the sub frames 501 to 504 are, forexample, arranged in the order of ascending retention period. The subframe may be further divided into a plurality of frames. That is,scanning of the gate signal line can be carried out at a plurality oftimes during the period of giving the same video signal.

An operation of a circuit illustrated in FIG. 14 is explained in a writeperiod and an erase period. First, an operation in a write period isexplained. In the write period, the gate signal line 911 at the i line(i is a natural number) is electrically connected to the write gatesignal line driver circuit 913. The signal line 911 is not connected tothe erase gate signal line driver circuit 914. The source signal line912 is electrically connected to the source signal line driver circuit915 via the switch 920. A signal is inputted to a gate if the firsttransistor 901 connected to the gate signal line 911 at the i line, andthe first transistor 901 is turned ON. At this time, a video signal issimultaneously inputted to the source signal line at the first row tothe last row. Video signals inputted from the source signal line 912 ateach row are independent to each other. Video signals inputted from thesource signal line 912 are inputted to a gate electrode of the secondtransistor 902 via the first transistor 901 connected to each sourcesignal line. Signals inputted to a gate electrode of the secondtransistor 902 controls ON/OFF of the second transistor 902. When thesecond transistor 902 is turned ON, voltage is applied to thelight-emitting element 903 and current passes through in thelight-emitting element 903. Emission or Non-emission of thelight-emitting element 903 is depending on a signal inputted to a gateelectrode of the second transistor 902. In the case that the secondtransistor 902 is a P-channel type, a light-emitting element 903 emitslight by being a Low Level signal inputted to a gate electrode. On theother hand, in the case that the second transistor 902 is an N-channeltype, a light-emitting element 903 emits light by being a High Levelsignal is inputted to a gate electrode of the second transistor 902.

Then, an operation in an erase period is explained. In the erase period,the gate signal line 911 (j is a natural number) is electricallyconnected to an erase gate signal line driver circuit 914 via the switch919. The gate signal line 911 is not connected to the write gate signalline driver circuit 913. The source signal line 912 is electricallyconnected to the power source 916 via the switch 920. A signal isinputted to a gate of the first transistor 901 connected to the gatesignal line 922 at the j line, and the first transistor 901 is turnedON. At this time, an erase signal is simultaneously inputted to thesource signal line at the first row to the last row. The erase signalinputted from the source signal line 912 is inputted to a gate electrodeof the second transistor 902 via the first transistor 901 connected toeach source signal line. By the erase signal inputted to the gateelectrode of the source signal line 912, the second transistor 903 isturned OFF and current supply from the current supply line 917 to thelight-emitting element 903 is stopped. The light-emitting element 903 isforced into non emission state. In the case that the second transistor902 is a P-channel type, a light-emitting element 903 does not emitlight by being a High Level signal inputted to a gate electrode. On theother hand, in the case that the second transistor 902 is an N-channeltype, a light-emitting element 903 does not emit light by being a LowLevel signal is inputted to a gate electrode of the second transistor902.

In the erase period, a signal for erasing is inputted by an operation asdescribed above at the j line. However, there is the case that the jline is an erase period and another line (the i line in this instance)is a write period. In this instance, it is required that a signal forerasing is inputted to the j line and a signal for writing is inputtedto the i line by utilizing a source signal line at the same row.Accordingly, an operation explained as follows is preferably carriedout.

Immediately after the light-emitting element 903 at the j−1 line is intoa non emission state by an operation in the erase state, the gate signalline 911 and the erase gate signal line driver circuit 914 are made intonon-emission states, and the source signal line 912 is connected to thesource signal line driver circuit 915 by changing the switch 920. Aswell as connecting the source signal line 912 to the source signal linedriver circuit 915, the gate signal line 911 is connected to the writegate signal line driver circuit 913 by changing the switch 918. A signalis selectively inputted to the gate signal line 911 at the i line fromthe write gate signal line driver circuit 913, and the first transistor901 is turned ON, simultaneously, a video signal for writing is inputtedto the source signal line 912 at the first row to the last row from thesource signal line driver circuit 915. By the video signal, thelight-emitting element 903 becomes in an emission state or non-emissionstate.

Immediately after finishing the write period of the i line as notedabove, lines move to an erase period at the j line. Hence, the gatesignal line and the write gate signal driver circuit 913 aredisconnected by changing the switch 918, simultaneously; a source lineand the power source 916 are connected by changing the switch 920.Further, the gate signal line 911 and the write gate signal line drivercircuit 913 are disconnected, simultaneously; the gate signal line 911is connected to the erase gate signal line driver circuit 914 bychanging the switch 919. A signal is selectively inputted to the gatesignal line at the f line from the erase gate signal line driver circuit914, and the first transistor 901 is turned ON, then, an erase signal isinputted from the power source 916. By the erase signal, thelight-emitting element 903 is forced into non-emission state.Immediately after finishing an erase period at the j line, lines move toan erase period at the i+1 line. Hereinafter, an erase period and awrite period may be carried out repeatedly to operate up to an eraseperiod at the last line.

In this example, a mode in which a write period at the i line, but notexclusively, is provided between an erase period at the j−1 line and anerase period at the j line is explained. A write period at the i linecan be provided between an erase period and an erase period at the j+1nline.

In this example, the erase gate signal line driver circuit 914 and acertain gate signal line are disconnected, simultaneously; an operationof connecting the write gate signal line driver circuit 913 to anothergate signal line is repeatedly carried out. Such the operation can becarried out in a frame that is not provided with a non-emission period.This example can be freely carried out with the foregoing example oranother example.

The light-emitting element according to the present invention canincrease the thickness of a passivation film without being adverselyaffected by peeling, cracking, or the like of the passivation film sincea stress relieving layer is formed on a top surface or a bottom surfaceof the passivation film. As a result, an extreme high blocking effectcan be obtained. Therefore, a light-emitting element having highreliability and long lifetime can be provided at high manufacturingyields. In the case that the stress relieving layer is formed over a topsurface (both surfaces) of the passivation film, the difference inrefractive indexes between the stress relieving layer and air can bereduced by forming the low refractive index layer to have a lowerrefractive index than that of the stress relieving layer. As a result,efficiency of light extraction to the outside can be improved.

The light-emitting element having the above noted operational advantagescan be adopted in a display device as typified by an EL display. Thedisplay device can be broadly divided into two kinds, that is, a simplematrix system in which an electroluminescent layer is formed between twokinds of stripe-shaped electrodes provided so as to be right angles witheach other, and an active matrix system in which an electroluminescentlayer is formed between a pixel electrode and an opposite electrodearranged in a matrix configuration and connected to TFT. Thelight-emitting element according to the present invention can be appliedto either of the simple matrix system and the active matrix system. Theforegoing display device can be applied to a ubiquitous goods such asvarious electronic appliances or an ID card, and so the industrialapplicability of the present invention is extremely large.

Although the present invention has been fully described by way ofexamples with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention hereinafterdescribed, they should be construed as being included therein.

1. A light-emitting device which has a pixel region having alight-emitting element, the light-emitting element comprising: areflective electrode over a substrate; an electroluminescent layer overthe reflective electrode, the electroluminescent layer comprising anorganic compound; a transparent electrode over the electroluminescentlayer; a first layer over the transparent electrode, the first layercomprising a material selected from silicon nitride, silicon oxide,silicon nitride oxide, and silicon oxynitride; and a second layer overthe first layer, the second layer comprising an inorganic material,wherein the first layer has a stacked structure comprising a third layerand a fourth layer, wherein the third layer comprises a materialselected from silicon nitride, silicon oxide, silicon nitride oxide, andsilicon oxynitride, and wherein the fourth layer comprises a materialselected from silicon nitride, silicon oxide, silicon nitride oxide, andsilicon oxynitride.
 2. The light-emitting device according to claim 1,wherein the reflective electrode comprises a metal.
 3. Thelight-emitting device according to claim 1, wherein the inorganicmaterial of the second layer is a material selected from siliconnitride, silicon oxide, silicon nitride oxide, and silicon oxynitride.4. The light-emitting device according to claim 1, wherein a refractiveindex of the second layer is smaller than a refractive index of thefirst layer.
 5. The light-emitting device according to claim 1, whereina refractive index of the second layer is smaller than a refractiveindex of the transparent electrode.
 6. The light-emitting deviceaccording to claim 1, further comprising a fifth layer over the secondlayer, wherein the fifth layer has a refractive index smaller than arefractive index of the second layer.
 7. An electric appliance which hasa display device including a pixel region, wherein the pixel regioncomprises a light-emitting element, the light-emitting elementcomprising: a reflective electrode over a substrate; anelectroluminescent layer over the reflective electrode, theelectroluminescent layer comprising an organic compound; a transparentelectrode over the electroluminescent layer; a first layer over thetransparent electrode, the first layer comprising a material selectedfrom silicon nitride, silicon oxide, silicon nitride oxide, and siliconoxynitride; and a second layer over the first layer, the second layercomprising an inorganic material, wherein the first layer has a stackedstructure comprising a third layer and a fourth layer, wherein the thirdlayer comprises a material selected from silicon nitride, silicon oxide,silicon nitride oxide, and silicon oxynitride, and wherein the fourthlayer comprises a material selected from silicon nitride, silicon oxide,silicon nitride oxide, and silicon oxynitride.
 8. The electric applianceaccording to claim 7, wherein the reflective electrode comprises ametal.
 9. The electric appliance according to claim 7, wherein theinorganic material of the second layer is a material selected fromsilicon nitride, silicon oxide, silicon nitride oxide, and siliconoxynitride.
 10. The electric appliance according to claim 7, wherein arefractive index of the second layer is smaller than a refractive indexof the first layer.
 11. The electric appliance according to claim 7,wherein a refractive index of the second layer is smaller than arefractive index of the transparent electrode.
 12. The electricappliance according to claim 7, further comprising a fifth layer overthe second layer, wherein the fifth layer has a refractive index smallerthan a refractive index of the second layer.